It is desirable to monitor location of certain people. Electronic monitoring is a tool for courts, penal institutions and hospital facilities, for example, to manage persons within their facilities and externally. Electronic monitoring may be used with offenders in pre-trial and post-release management of the person monitored. Use of electronic monitoring instead of imprisonment reduces prison population and provides a convenient way of verifying that the offender obeys conditions of release.
Often an offender will have a home detention curfew imposed requiring the offender to stay within his or her place of residence during specific hours. For example, the offender may be required to remain within their place of residence from 6 pm to 7 am each day. Non-compliance with this requirement is a breach of curfew. Where curfew is breached, the offender may be summoned to court, whereupon more severe punishments may be imposed.
A monitoring system is required to monitor compliance with home detention curfews. Such a system may comprise the tracking device, a residence monitoring unit (RMU) and a remote monitoring platform. The tracking device securely attaches to the offender, usually around the offender's ankle, but in some instances the tracking device may be worn around the waist or wrist. The tracking device is designed to prevent removal by the offender. The monitoring system is configured so that any removal or serious attempt at removal of the tracking device is detected. The removal or serious attempt at removal is considered as a breach of curfew.
The RMU is installed in the offender's place of residence. The tracking device contains radio technology allowing communication with the RMU, so that it can be determined whether the tracking device is within a predetermined range of the RMU, which defines the area over which the offender can move. To maintain communication with the RMU, the tracking device polls the RMU and the RMU listens for polls. Through this polling, the RMU is able to detect whether or not the tracking device is within range since, if polls are not received, the offender is considered to have left his or her place of residence.
The RMU is configured to report data on the polling to the remote monitoring platform. The remote monitoring platform is a computer system that is configured to receive the polling data from the RMU. The polling data is accessible by enforcement persons. The monitoring platform may be configured to perform analytics upon the polling data so that information available to the enforcement persons is more useful. The particular analytics performed depends upon the purpose and functionality of the remote monitoring platform. For example, a simple remote monitoring platform may notify enforcement persons of non-compliance with a home detention curfew in real-time. A more sophisticated system may also store all compliance and non-compliance data and automatically generate detailed reports based on the data.
It is to be noted, that installation and de-installation of the RMU and the tracking device is expensive, not only due to the cost of the RMU and a tracking device but also due to labour costs. Lengthy periods may be required to be spent in offender's homes, which may, on some occasions, be hazardous.
Generally, leaving aside installation and de-installation, electronic monitoring systems are configured to automatically monitor offenders and the only manual intervention required is to investigate non-compliance with terms of the monitoring. Typically, investigating a non-compliant event involves a representative from a monitoring organisation (typically referred to as a “Field Officer” (FO)) visiting the offender's home. The FO may find that the offender has absconded, in which case the police are notified so that the offender can be tracked down, which is clearly a laborious and expensive process. The FO may find that the offender is still within their home. This may be due to the offender having left home briefly and returned. It may alternatively be due to a breakdown of the communication between the tracking device and the RMU. In this case, it may instead be due to a blind spot.
Blind spot may arise due to uneven distribution of RF signal from RMU, such that in some areas the signal is weaker than expected. Thus, the offender may be located within their home when no RF link is possible between the RMU and the tracking device. Also, blind spots exist where the polling signal produced by the tracking device is not received by the RMU.
The uneven signal distribution is caused by several factors present within all homes. These factors include the existence of interior walls, electrical equipment, furniture and metallic objects. For example, blind spots may be caused inside buildings by multiple RF beams bounced off walls. In some cases, these beams combined their energy and boost the signal in a particular place in the building; in other cases the opposite occurs and blind spots are formed in the building where the signal is too weak for detection.
One possible way to attempt to reduce blind spots is for the RMY and preferably also the tracking device to produce a more powerful radio signal. A more powerful radio signal reduces the number of blind spots within a home and may reduce the size of others; however it is unlikely to completely eliminate them. Furthermore, the main purpose of the electronic monitoring system is to detect movement of the offender out of the area of his or her home, where the area of the home is defined by the range to which the offender can move with the RMU and the tracking device maintaining a link. If the power of the radio signal is increased, the area over which the offender can move is increased, potentially thereby not restricting the offender to their home, but to a wider area. For example, for some residences, the power may need to be increased to such a level that it is possible for the offender to be 500 meters or more from their place of residence without a breach of curfew being detected and reported, in order for the number of blind spots and their size to be usefully reduced.
Another possible way to reduce the problem of blind spots is to use more than one RMU in the offender's at home. This greatly reduces the likelihood of blind spots existing and allows the range of the RF signal to be more accurately controlled without the power of an RMU antenna being significantly increased. There are however various disadvantages to using multiple RMUs. Costs relating to the RMUs are multiplied. Use of multiple RMUs does not guarantee that blind spots will be eliminated. Different numbers of RMUs are required for different sizes and/or layouts of homes. Installation is more laborious. The consistency of the RF signal through the home has to be verified by a trained technician, adding time and cost to the installation process and also introducing greater possibility for human error. Where the RMUs communicate to the remote monitoring platform over radio telephone landline, their location in a home is limited to areas in which telephone jack points are located. Further, many homes do not have a sufficient number of suitable telephone jack points. This may be particularly problematic as it is recommended that RMUs are installed away from certain appliances, such as televisions, microwaves, sources of moisture, direct sunlight, washing machines, radiators and places where they may be vulnerable to being knocked.
Another possible way to reduce or eliminate blind spots is to use multiple antennas separated in space within a single RMU, using so-called multiple input multiple output (MIMO) technology. Such technology is widely used to mitigate the effects of RF interference. MIMO systems advantageously reduced occurrence of blind spots. However, use of such technology significantly increases the size of the RMU as well as its cost, without guaranteeing elimination of blind spots.
It is an object of the present invention to mitigate the effects of blind spots, without any of the drawbacks mentioned above.